2o8** 
NOTE 
is almost entirely among the seedlings and young plants, in 
which these characters are not yet present. In many genera in 
the tropics, the young plants are almost exactly alike, and the 
distinguishing characters may not appear till the plants are 20 
to 40 years old, when the struggle for existence must be long 
over, so far as concerns other members of the same species, 
though there will still be a struggle with the immediate 
neighbours, which in the tropics are usually of different species, 
and only rarely of the same. 
Again, any one plant can on the average only have six 
competitors surrounding it, and the struggle, though it may be 
very strenuous, cannot cover plants having a very wide range 
of variation, so that any improvement due to selection of 
variations must be almost indefinitely less than is often sup- 
posed. 
Or the new theory may be applied to such questions as 
geographical distribution. In such a continent as Indo-malaya, 
the general form of distribution is to have a few widely ranging 
common species, with nearly allied forms scattered along their 
range and endemic to one district. It is far more easy to get 
such distribution by supposing the common species to mutate 
off the others, than by any theory of infinitesimal variation upon 
which a vast amount of destruction, for which we have no 
warrant, is necessary. Further, the distribution of tlie whole 
order can be more easily understood, for there is no need to 
assume the destruction of ancestral types, but one may have the 
whole tree of the order perhaps existing at present, eg. all the 
Dilleniaceae may be supposed to have descended from Tetra- 
cera, a genus still existing and very widely spread. 
The following literature may be consulted ; in addition to 
that already quoted : 
de Vries, Species and Varieties , their origin by Mutation ; 
trans. by Macdougall : London, 1905. 
de Vries, Die Mutations-theorie : Leipzig, 1905. 
de Vries, Plant Breeding : London, 1907. 
Lock, Recent progress in Heredity and Evolution; London, 
1907. 
Gulick, Evolutio?i , Racial and Habitudinal : Washington, 
1905. 
Willis, Some evidence against the origin of species* by infini- 
tesimal variation..., Ann. Perad. IV, 1907, p. 1 ; Further 
evidence..., do. p. 17; The Geographical Distribution of 
the Dilleniaceae..., do. p. 69. 
